1. Field of the Invention
The present invention relates to feeding apparatuses and, more particularly, to a feeding apparatus for use in image forming apparatuses and image reading apparatuses such as a copying machine and a printer or the like.
2. Related Background Art
FIG. 13 is a schematic sectional view of a manual sheet feeding apparatus capable of continuous sheet feeding using a retard separation system according to a conventional art.
Referring to FIG. 13, reference numeral 102 denotes a pick-up roller driven and controlled by a conveyor clutch 108 for rotation and suspension of rotation, so as to feed a sheet S carried on a sheet feeding tray 101 one by one. After the sheet S is transported to a separation position between a separating roller 104 and a sheet feeding roller 103, a pick-up solenoid 106 causes the pick-up roller 102 to be detached from the sheet S.
This detachment is necessary to ensure that, in the case where a plurality of sheets are transported to a separation position at the time of a pick-up operation by the pick-up roller 102 (hereinafter, such a situation will be referred to as double feeding), the double feeding can be certainly prevented by not hindering any reverse force of the sheet which is double fed at the time of separation by the separating roller 104.
Moreover, in a non-active state of the main system, the pick-up roller 102 is also caused by the pick-up solenoid 106 to be detached from the sheet to ensure that the pick-up roller 102 does not hinder a setting operation performed by a user.
Additionally, a shutter 110 activated only when a sheet feeding apparatus is in a non-active state is provided to ensure that a user""s inappropriate operation performed in setting a bundle of sheets does not cause the bundle of sheets to advance to the separation position and to provide the user with a feedback pressure so that the inappropriate setting operation does not cause a malfunction of the pick-up operation. The shutter solenoid 107 causes the shutter 110 to operate properly.
As described above, the manual sheet feeding apparatus according to the conventional art that employs the retard separating system requires the pickup roller 102 for feeding the sheet S one by one from the bundle of sheets. Further, a mechanism for detaching the pick-up roller 102 from the sheet, implemented by the solenoid 106, is necessary not to hinder any setting operation.
The shutter 110, which prevents the user""s inappropriate operation, and the shutter solenoid 107 for controlling the shutter 110 are necessary.
Consequently, the requirement for space for housing the system may grow significantly, the construction may become complex and the cost of manufacturing may become relatively expensive.
Another disadvantage is that, in the construction described above, the driving and control of the pick-up roller 102 for rotation and suspension of rotation, as well as the control of the pick-up roller 102 for elevation and lowering require the conveyor clutch 108 and the shutter solenoid 106. Therefore, the likelihood that an error is produced in actuating the conveyor clutch 108 and the shutter solenoid is relatively great. As a result, the operation of the sheet feeding apparatus may be improperly timed, thereby causing double feeding or paper jam.
For example, the detachment of the pick-up roller 102 should be properly timed to occur when the leading edge of the sheet S reaches a nip between the sheet feeding roller 103 and the separating roller 104. Otherwise, delayed feed paper jam occurs. The detachment of the pick-up roller 102 should also occur before the leading edge of the sheet reaches a feed roller pair 105 provided downstream. Otherwise, the pick-up roller 102 loses the chance to force the sheet backward, thus causing double feeding. Thus, double feeding or paper jam is caused.
Moreover, timing requirement for the control of the conveyor clutch 108 and the solenoid 106 is so great as to make the control procedure extremely complex.
The present invention has been developed in view of the disadvantages described above and has an object of providing a sheet feeding apparatus and an image forming apparatus provided with the same, in which the cost and size are reduced by simplifying the construction, and in which proper timing is maintained and the stable sheet feeding and separation are performed. A typical components of the apparatus include displaceable sheet supporting means for supporting sheets; a feeding rotation body for feeding the sheet forward by contacting the sheet supported by the displaceable sheet supporting means and rotating in a direction of transportation of the sheet; and a separating roller pressed against the feeding rotation body and rotated in a direction to force the sheet fed by the feeding rotation body backward so as to separate the sheet. The sheet supporting means, the feeding rotation body and the separating rotation body are disposed such that an angle xcex8 satisfies a condition 15xc3x97(xcfx80/180) rad (=15xc2x0)xe2x89xa6xcex8xe2x89xa650xc3x97(xcfx80/xcfx80180) rad (=50xc2x0), where xcex8 denotes an angle between a line tangent to the feeding rotation body when the sheet supporting means is displaced to cause the topmost sheet supported by the sheet supporting means comes into contact with the feeding rotation body, and a nip line of a nip where the feeding rotation body and the separating rotation body are pressed against each other.